The invention relates to a knife with blade that moves relative to the handle. The demand made on a knife with a driven blade is that it substantially reduces the necessary expenditure of force when cutting a product compared with knives with a non-driven blade and thus also the time involved, for example when boning a slaughtered animal.
In the case of a knife belonging to the prior art (DE-GM 89 08 775 U1), the driven blade is attached to the working piston outside the knife handle. This results in insecure guidance when using the knife, because a pressure is exerted on the blade in the cutting process which tends to press the blade out of its path. The number of tasks which can be performed with such a knife is thus limited, for only a straight cut is feasible with such a knife but no curved cutting as is required, for example, for boning a slaughtered animal. In order to save weight in this knife, the blade of this knife is moreover of very thin design, as a result of which the poor guidance characteristic of the knife is further increased. For this reason a support for the blade is provided, which is also located outside the knife and therefore substantially disturbs the use of the knife, because this support comes into contact with the meat in the cutting process and bruises it.
A knife with a driven blade according to CH-PS 224 265 is also known, in which the blade is driven by means of an electromagnet. The guide of the blade is located in the handle of this knife, but kept extremely short, as a result of which the blade has no secure bearing, so that the same disadvantages occur as in the knife mentioned above, namely that it cannot be securely guided. Furthermore, in the case of the knife according to CH-PS 224 265, the entire drive must be dismantled from the handle in order to change the blade, which is complex and time-consuming, especially as the blades must be frequently reground when the knife is used for commercial purposes, for example for boning a slaughtered animal, because they are subject to heavy wear and have to be replaced.
The electromagnetic drive moreover does not permit the blade to be driven with great force unless a correspondingly large magnet is selected. Such a large magnet, however, makes the knife unwieldy on account of its volume and is much too heavy.
According to EP 0 241 385 A1, a knife with a blade moved in a chisel-like way is known, which is used mainly for opening shellfish. In the case of this knife, the blade is to execute strong thrusting movements in one direction, namely away from the knife handle.
The thrusting movements are effected by a piston which can be moved to and fro by air-pressure fluctuations, which strikes, when the blade is in working position, against an anvil which is permanently connected with the blade and moves the latter forward in thrust direction.
This knife is not intended for cutting, for example for boning slaughtered animals, because a pressing movement in axial direction of the blade is implied in this case but the load on the blade is transverse to this direction of motion when the knife is being used for cutting. Knives for cutting purposes normally have a tang located in the handle of the knife.
Among the professional public and according to the invention, the term "tang" is understood as an extension of the blade, normally in the form of the blade, which extends into the inside of the knife handle and acts there as a fixing medium. In the context of the invention, the effect of the provided tang is that the blade moves in a stable and secure manner to and fro in the special guide provided in the handle of the knife.
This secure and stable guidance of the tang according to the invention cannot be attained by attaching the blade directly to the anvil according to EP 0 241 385 A1 with the functional efficiency striven for by the invention.
Furthermore, measures for replacing the blade are not to be drawn from EP 0 241 385 A1. Obviously the entire knife must be dismantled for this purpose, so that the same disadvantages occur as in the knife according to CH-PS 224 265.